This invention relates generally to a fluid system, and more particularly, to a method and apparatus for controlling a deadband of a fluid system.
Fluid control systems located on work machines include an operator interface for enabling the operator to control the fluid system and a hydraulic circuit for controlling the work implements of the machine in response to the operator""s inputs. The operator interface may include joysticks adapted to receive the operator inputs and generate the appropriate input signals to control the fluid system. A controller receives the inputs signals and determines the appropriate valve commands. The valve commands are delivered to a valve assembly, or control valve, which controls the fluid flow from a pump to an actuator. The valve assembly may include a pilot valve and a main valve.
An implement of a work machine is connected to one or more actuators through linkages having a linkage position associated with the position of an implement. For example, in a track-type tractor, the movement of the blade is controlled in several directions. The blade may be lifted or lowered by pivoting a C-frame about a linkage point on a main frame of the tractor. The blade may be pitched by pivoting a linkage point on the blade with respect to the C-frame.
The controller determines a valve command in response to the operator input signal and associated hydraulic circuit signals, such as the signal received from an engine speed sensor. The valve command signal is then delivered to the appropriate valve assembly. In some machines, the valve command signal may be delivered to the solenoid of the pilot valve located within the valve assembly. The solenoid is then energized and controls the valve spool within the pilot valve to-achieve an appropriate position in response to the valve command signal. The pilot valve then responsively delivers a pilot pressure to the main valve in order to move the main valve, or the spool within the main valve, to the desired position. The main valve then enables fluid to be delivered to the actuator.
In a fluid control system, there is a deadband associated with the movement of the joystick from a neutral position to a position where an initial movement of the actuator being controlled occurs. This deadband may be referred to as a first motion deadband. The deadband may be associated, in part, with the change in valve position needed in order to provide an appropriate amount of fluid flow to the actuator in order to initiate actuator movement.
The responsiveness of the actuator may be dependent, in part, on the fluid pressure and fluid flow rate delivered to the actuator. The fluid pressure and fluid rate may in turn be dependent, in part, on the main valve position, engine speed, and pump displacement.
A first motion deadband represents the amount that the main valve stem must move before the associated actuator, for example, a cylinder, moves due to fluid pressure. The first motion deadband also corresponds with movement of the joystick from an initial position of the joystick to a position where the initial movement of the actuator occurs. The amount of movement of the joystick corresponding with the first motion deadband may be programmed to meet operator specifications. This amount of movement is generally consistent for a given engine speed, pump displacement, and load. However, if the pump engine speed is reduced, for example, from a high idle to a low idle speed, then the same joystick command at the high idle speed will not cause the same response of the actuator at the low idle speed. Therefore, the joystick command will need to be increased, for example, as the engine speed is reduced, in order to provide enough fluid flow to the actuator to achieve the same actuator response as in the high idle condition.
Some conventional fluid systems account for these various factors, including certain load-induced, operating conditions, that may cause deadband inconsistencies. For example, U.S. Pat. No. 5,784,945 to Krone et al. discloses a system having a desired velocity manager and a load responsive device that determine a desired velocity of a load and a characteristic of the load, for example, weight. The desired velocity and load characteristic are used to determine a valve transform curve, which is then used to control operation of a valve that controls fluid flow to an actuator operating on the load.
However, other operating conditions, for example, linkage position, may also cause variations in the first motion deadband. Variations in first motion deadband may result in an inconsistent operator interface, which reduces the efficiency of the operator. Moreover, such variation may lead to errors in the operation of the machine.
The present invention is directed to overcoming one or more of the problems identified above.
A first exemplary embodiment of the invention provides a method for controlling a fluid system. The system may include a hydraulic circuit having a pump driven by an engine, wherein the pump delivers fluid to an actuator through a valve assembly. The method may include receiving an operator input and determining a condition of the hydraulic circuit. The condition of the hydraulic circuit may include at least one of a rate of fluid flow to the actuator, an engine speed, and a pump displacement. The method may further include determining a valve transform function as a function of the condition of the hydraulic circuit and a position of a linkage associated with the actuator. The method may include determining a valve command in response to the valve transform function and the operator input and delivering the valve command to the valve assembly.
Another exemplary embodiment of the invention describes a method for controlling a fluid system. The system may include a hydraulic circuit having a pump driven by an engine, wherein the pump delivers fluid to an actuator through a valve assembly. The method may include establishing a first motion deadband, receiving an operator input, determining a position of a linkage associated with the actuator, and determining a rate of fluid flow to the actuator. The method may further include determining a valve command in response to at least one of the fluid flow rate, the linkage position, the first motion deadband, and the operator input, wherein the valve command may result in a consistent deadband.
According to another exemplary embodiment of the invention, a fluid system may include a hydraulic circuit having a pump, an engine structured and arranged to drive the pump, an actuator, and a valve assembly operable to control flow of pressurized fluid from the source of pressurized fluid to the actuator. The system may further include a linkage associated with the actuator and an input controller configured to receive an operator input and responsively generate an input signal. A controller may be configured to receive the input signal, a linkage position signal, and at least one of a flow rate signal corresponding to fluid flow to the actuator, an engine speed signal, and a pump displacement signal. The controller may also be configured to determine a valve transform function in response to the linkage position signal and at least one of the fluid flow rate signal, the engine speed signal, and the pump displacement signal. The controller may be further configured to determine a valve command in response to the input signal and the valve transform function, the valve command resulting in a consistent deadband.
The foregoing summarizes only a few aspects of the invention and is not intended to be reflective of the full scope of the invention. Additional features and advantages of the invention are set forth in the following description, may be apparent from the description, or may be learned by practicing the invention. Moreover, both the foregoing summary and the following detailed description are exemplary and explanatory and are intended only to provide further explanation of the invention.